The popularization of computers and the networking of information have been accompanied by the wide use of e-mail for sending and receiving text information over networks. In addition to the body of mail, which is text information, files having various formats can be attached to e-mail, and there has been proposed an Internet fax (referred to also as “IFAX” below) in which images can be sent and received by attaching an image file having a format (TIFF: Tagged Image File Format) defined as an attached file.
According to RFC2532 (Expanded Facsimile Using Internet Mail) issued by the Internet technology development group IETF (Internet Engineering Task Force), which is engaged in standardizing Internet technology, there has been proposed a so-called “full mode” for Internet fax, wherein when mail to which a TIFF file transmitted by a transmitter has been attached is received normally by a receiver, the fact that reception proceeded normally is reported from the receiver to the transmitter in the form of e-mail.
When an e-mail server handles e-mail having a large data size, processing speed declines sharply and the distribution of other e-mail is impeded. In a worst-case scenario, the mail server goes down and the e-mail system can cease functioning.
For this reason, a technique whereby e-mail data is divided into a plurality of segments at the time of transmission has been proposed, as described in the specification of Japanese Patent Application Laid-Open No. 2002-324035.
Further, the specification of WO03-067440 (corresponding to Japanese Patent Application Laid-Open No. 2003-233558) proposes providing a switch whereby e-mail is switched between transmission via a SMTP server or transmission directly to the destination, with the changeover being performed for every transmission destination that has been set in an address book.
Because there is an increase in processing load (a decline in processing speed) when an e-mail file having a file attachment of large data size is sent and received, as mentioned above, there are cases where the mail server imposes a limitation upon the data size of e-mail. A problem which arises in such cases is that image data of large data size cannot be transmitted. In addition, often the limitation on data size differs from one mail server to another.
Further, in a case where the transmission destination is in an Internet environment in which a firewall or the like exists along the transmission path, transmission via a mail server is required. However, in the case of a local environment in which the transmission destination exists on the same network, transmission via a mail server is unnecessary. In such case, therefore, it is not necessary to abide by a data size that is capable of being accepted by the mail server.